We evaluated the response of Kentucky bluegrass (Pea pratensis L.) turf to urea amended with the urease inhibitors PPD, NBPT, and ATS and with the cations K+ (KCl) and Mg+2 (MgCl2). Treatments for the 2-year field experiment included liquid urea applied monthly in June to Sept. 1985 and 1986 at 49 kg N/ha with PPD (1%, 2%, 3% by weight of applied N), NBPT (0.5%, 1%, 2%), ATS (5%, 15%, 25%), K+ (5%, 15%, 25%), and Mg+2 (5%, 15%, 25%). The NBPT was included only in the 1986 field study. The Mg+2 and K+ reduced foliar burn and increased turf quality during mid- and late Summer 1985 at the 5% rate, but clipping yield was not affected by any treatment. In 1986, under milder climatic conditions, PPD and NBPT increased clipping yield by 13.2% and 15.2%, respectively. At the 15% rate, ATS increased clipping yield by 15.1%, but, on average, PPD and NBPT were much more effective. Chemical names used: phenylphosphorodiamidate (PPD), N-(n -butyl) thiophosphoric triamide (NBPT), and ammonium thiosulfate (ATS).